On Wed, Mar 18, 2009 at 8:58 AM, Yu, Changhong <y...@ccf.org> wrote: > Dear all, > I am totally confused by the following R output, but don't have a clue > for it. > >> a <- 1 - 0.2 > >> a == 0.8 > > [1] TRUE > >> a <- 1 - 0.8 > >> a == 0.2 > > [1] FALSE
This is expected behaviour. The bottom line is that you shouldn't rely on the equality operator when dealing with floating point values in any numerical software, including R. I write about this in detail at: http://blog.revolution-computing.com/2009/03/when-is-a-zero-not-a-zero.html which will hopefully clear up your questions. # David Smith -- David M Smith <da...@revolution-computing.com> Director of Community, REvolution Computing www.revolution-computing.com Tel: +1 (206) 577-4778 x3203 (Seattle, USA) Check out our upcoming events schedule at www.revolution-computing.com/events ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
